Feed screw mechanism



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March 6, 1945.

QN. LIN

TTORNEY.

Patented Mar. 6, 1945 FEED SCREW MEcHANIsM Bengt R. Granberg and Gustaf H. Ekstrom, Rockford, lll., assignors to Sundstrand Machine Tool Co., Rockford, Ill., a corporation of Illinois Application March 13, 1940, Serial N0. 323,780

(Cl. .S- 22) 4 Claims.

This invention relates generally to improvements in feeding mechanism for machine tool supports or work tables, and more particularly to an improved screw and nut device in which lost motion or back-lash between the parts is effectively prevented.

' It is the general object of the invention to provide a new and improved feed screw mechanism of the screw and nut type, which is simple in construction and efficient in operation, and which will effectively prevent lost motion between the parts during operation.

Another object of the invention is to provide an improved feed screw mechanism arranged to prevent lost motion during operation of the feed screw in either direction.

A further object is to provide a feed mechanism of the screw and nut type, in which the nut element includes two parts, both engaged with the screw element but relatively adjustable along the axis of the screw for taking up backlash or lost motion, and in which the surface of `one of said elements is composed of a special material such as chromium plate, serving to minimize friction between the screw and nut elements, and insuring long, useful life therefor, so that means for effecting the adjustment may-permissibly act with sufcient force to create a relatively high pressure between the threads of the respective elements.

Other objects and advantages will become apparent from the following description taken in connection with the accompanying drawing, in which: Y

Figure 1 is a vertical section taken through the base table of a milling machine at the axis of the feed screw, and illustrating a preferred form of the invention embodied therein.

Figure 2 is a transverse detail section taken as indicated at line .2-2 on Figure 1 to show the adjusting means for the take-up nut.

Figure 3 is a fragmentary detail section taken at the same plane as Figure 1 and showing a modified form of take-up nut.

4While there is shown in the drawing, and described herein, a preferred form of this invention as embodied in a screw and nut feed mechanism for actuating the work table of a milling machine, it is to be understood that the invention is not limited to the specic form or application thus disclosed, and that we intend to cover all modifications and alternative constructions falling within the spirit and scope of the invention, as expressed in the appended claims.

As illustrated in the drawing, the table or work .dition by means of end caps I4?, and the screw being provided with clamping nuts 38- which act against the inner races of thebearings to place the screw under a normal working tension. This prevents end play between the screw and table I0, and also subjects the screw to an initial elongation, thereby eliminating lost motion in the screw itself.

The base frame II supports a nut element I5 threaded to engage the screw I3 and formed with a flange I5a at yone end; its oppo-site end is threaded and provided with a clamping nut' I6 by which the nut I5 is held fixed against, axial movement in the frame II. A key I'I engaging a groove I8 in the outer surface of the nut I5 l taking up lost motion or back-lash. One end of` locks it against rotation.

A second and supplemental nut 20, also threaded to t the screw I3, is mounted in the base frame II engaging the screw at a distance from the nut I5. The nut 20 is held against 4 rotation in the frame II by means of a key 2| engaging a groove 22 in its surface, but it is adjustable along the axis of the feed screw I3 for the nut 20 is of reduced diameter, and is formed with a relatively fine thread at 20a. The adjusting nut 24, carried by the threads at 20a, is formed as a worm gear with peripheral teeth 25 meshing with a worm 26 which is journaled in a portion of the base frame II, as shown in Figure 2. The shaft 21 of the worm 26 includes a flange or collar 28 and a clamping nut 29 which may be employed to lock the worm against rotation when it has been operated bymeans of a suitable wrench or crank applied to the squared end 30 of the shaft 2l. By 'means of the worm 26 and nut 24, the nut 20 may be slidably shifted along the axis of the feed screw I3 so as to take up any looseness or back-lash in the engagement of the threads of the screw I3 with those of the nut I5. Preferably, this adjustment of.

the nut 20 is in a direction away from the head or flange I5a of the nut I5 so as to exert a tension on that portion of the feed screw between the nuts I5 and 20.

In the design illustrated the nuts I5 and 20 are mounted'on the base II at opposite sides 2 of a feed box 30" within which there is rotatably mounted a gear 3| which has a splined connection with the feed screw I3. 'I'his gear meshes with a second gear 32 which, in turn, meshes with a driving gear 33 loperated by a driving shaft 34 leading from any suitable power connection, not shown. ThusV the rotation of the gear 3I turns the feed screw' I3 and causes it to travel along its axis through the nuts I5 and 20, moving the table I upon the frame Il, and

reverse rotation of the gear 3I will shift the table f in the opposite direction. In addition, the ends of the screw shaft I3 are squared at 35 to receive also anchored against rotation by means of a key 4I engaging a groove 42 in its outer surface.

v'I'he nut 40 is formed with reduced and threaded portions 43 at both ends, with clamping nuts 44 and 45 applied respectively-to these threaded end portions and engaging against opposite faces'of the part of the base frame II in which the nut 40 is slidably mounted. Thus the nuts 44 and 45 may be adjusted to shift the nut 40 along the axis of the screw I3 for taking up lost motion or back-lash, and preventing end play of the screw I3 in the base frame II. It will be evi-f dent that this modified construction may be a little'cheaper to manufacture than that shown in Figures 1 and 2, vbut that in many instances it could not be made as conveniently accessible for adjustment.

Ordinarily, the tightening of the adjustable nut 20 (or the nut 40) 4to such an extent as to exert any considerable tension along the axis of the feed screw I3 in taking up `the play or backlash in the threads thereof, would create excessive fri'ction between the threads of the screw I3 and those of the nuts I and 20, which would impose a severe load upon the drive mechanism,l

and might either stall the operation of the machine or result in very rapid wear of the threaded elements of the feed mechanism. However, we have discovered that if the threads are chromium-plated the co-ecient of friction is so greatly reduced that a very considerable stress may be exerted against the threads by adjustment of the nut (or the nut 40)` without hampering operation of the machine, and without shoulder bearing against a part of the base and the second nut having a threaded portion with finer threads than the feed' screw and with an adjusting nut thereon, said adjusting nut having a transaxial =`surface facing toward said shoulder of the rst nut and bearing against a part of the base whereby the second nut may be adjusted along the axis of the feed screw relativelyto the rst nut and in a direction to exverts a tension on the screw, together withmeans positively locking said adjusting nut'against rotation.

2. In a machine tool which includes a base, a

member mounted for reciprocation on said base,

any rapid deterioration of the threaded members through wear. Preferably, the chromium-plating is applied to the surfaces of the feed screw I3, and the nuts I5 and 20 are made from a suitable quality of bearing bronze or other alloy, so that when these parts eventually become worn in service they can be economically replaced.

We claim as our invention: v

1. In a machine tool which includes a base, a member mounted for reciprocation on said base, and a feed screw rotatably journaled on said member, the 4combination of a nut engaging the feed screw and secured xedly to said base, and a second nut engaging the feed screw and secured `positively in said base against rotation, the nrst nut having an' integral transaxial and a feed screw rotatably journaled on said member, the combination of a nut engaging the feed screw and secured ixedly to said base, and a second nut engaging the feed screw and secured positively in said base against rotation, the first nut having an integral, transaxial shoulder bearing against a part of the base, and the second nut having. athreaded portion with finer threads than the feed screw and with an adjusting nut thereon, said adjusting nut having a transaxial surface facing toward said shoulder of the rst nut and bearing against a part of the base, together with gear teeth on the adjusting nut and a rotatably mounted worm meshing with said teeth Afor rotating the nut and locking it against rotation, whereby the second nut may be adjusted ,along the. axis of the feed screw relatively to the first nut and in a direction/t0l exert a tension on the screw.

3. In a machine tool which includes a base, a

,- member mounted for reciprocation on said base,

and a feed screw vrotatably journaled on said member, the combination of a nut -engaging the feed screw and secured Xedly to said base, and a second nut engaging the feed screw'and secured positivelyin said base against rotation,the iirst nut having a transaxial shoulder bearing against a part of the base and the second nut having a threaded portion with an adjusting nut thereon, said adjusting nut having a transaxial surface facing toward said shoulder of the first nut and bearing against a part `of the base'whereby the second nut may be adjusted along the .axis of the feed screw relatively to the rst nut and in a direction to exert a tension on the screw.

4. In a machine tool which includes a base, a member mounted Vforreciprocation on said base, and a feed screw rotatably journaled on said member, the combination of a nut engaging the feed screw and secured iixedly to said base, and

al second nut engaging the feed screw and secured positively in said base against rotation, the first nut having a transaxial shoulder bearing against a part of the base and the second nut the feed screw relatively to the rst nut.

BENGT R. GRANBERG. GUSTAF H. EKSTROM. 

